1. Field of the Invention
This invention relates to an improved process for producing 2-methyl-1,4-naphthoquinone (menadione, vitamin K.sub.3 ). More particularly, it relates to a process for producing 2-methyl-1,4-naphthoquinone which comprises reaction of a 1-lower-alkoxy-2-methylnaphthalene with hydrogen peroxide in the presence of a hexacyanoferric acid or a salt thereof as catalyst.
2. Description of the Prior Art
A method is known for producing 2-methyl-1,4-naphthoquinone, in which 2-methylnaphthalene is oxidized with chromium trioxide [P. P. T. Sah, Rec. Trav. Chim., 59, 1021 (1940)]. An improvement thereto was also proposed, in which a special apparatus called "film reactor" is used to prevent excessive oxidation by chromium trioxide [H. Veldstra and P. W. Wiardi, Rec. Trav. Chim, 62, 75 (1943)]. These methods are not satisfactory for commercial production because chromium trioxide (a substance which can be an environmental harzard) is used and the product yield is rather low (29% for the former, and 45% for the latter).